The optical semiconductor component package is included in an optical pickup device which carries out reading and writing for optical discs. The semiconductor package has a light emitter which emits light to an optical disc, a diffraction grating which diffracts reflection light from the optical disc, and a photoreceptor which detects the light diffracted by the diffraction grating, and the like.
As an example of the described semiconductor package, the following will explain the arrangement of a semiconductor laser package disclosed in Japanese Patent Publication No. 3035077 (published on Jan. 14, 1994). FIG. 6 is a plan view of this conventional semiconductor package, and FIG. 7 is a perspective view of the package.
This package includes a semiconductor laser chip 104 for emitting a laser beam, a PIN photodiode 105 for monitoring the laser beam of the semiconductor laser chip 104, and a photodiode 106 for receiving the reflection light from an optical disc, on a component bearing surface of a stem 101. Further, a cap 102 is provided to cover these optical elements and a glass substrate 103 having an optical deflecting diffraction grating is provided in a hole which is formed in the edge of the cap 102. Further, a laser beam emission glass window 107 is formed on the cap 102.
Here, the semiconductor laser chip 104 is disposed in the center of the component bearing surface of a stem 101. Further, the photodiode 106 is disposed on one side of the semiconductor chip by keeping a distance from the semiconductor laser chip 104. The optical deflecting diffraction grating of the glass substrate 103 makes the reflection light from the optical disk incident onto the photodiode by diffracting the reflection light from the optical disk.
Two opposed circular-arc parts 101a and 101b, and two opposed straight-line parts 101c and 101d make up the outline of the component bearing surface of the stem 101. The circular-arc parts 101a and 101b are provided symmetrically with respect to the center of the component bearing surface of the stem 101, where the semiconductor laser chip 104 is provided. With this arrangement, by holding the circular-arc parts 101a and 101b of the stem 101 so that the stem 101 can rotate, it is possible to rotate the stem 101 without shifting an optical axis of the semiconductor laser chip 104.
In the optical pickup device having this semiconductor package, it is possible to accurately read a servo signal of the optical disc, as the stem 101 is rotated by thus holding the circular-arc parts 101a and 101b of the stem 101.
Further, the following will explain the arrangement of another optical pickup device, which is disclosed in Japanese Unexamined Patent Publication No. 2000-123433 (published on Apr. 28, 2000). FIG. 8 is a cross-sectional view of this conventional optical pickup device.
This optical pickup device includes:                a semiconductor laser 201 which emits a laser beam;        a second diffraction grating 216 which divides the laser beam from the semiconductor laser 201 into three or more light beams;        a lens (not shown) which collects the laser beams divided by the second diffraction grating 216 on an optical disc;        a beam splitter 202 which splits reflection light from the optical disc into differently polarized components;        a first diffraction element 206 which diffracts a part of the reflection light split by the beam splitter 202; and        a photoreceptor 207 which receives the reflection light which is split by the beam splitter 202 and partly diffracted by the first diffraction element 206.        
One of the three beams divided by the second diffraction grating 216 is used as a main-beam for reading out data from the optical disk and writing data on the optical disk, and the other two are used as sub-beams for carrying out tracking servo of the optical pickup device. These three beams make three light spots on the optical disk. Namely, the tracking servo is performed by a so-called three beams method.
The reflection light from the optical disc is incident onto a polarization split element 204 after being reflected by a reflection surface 203 of the beam splitter 202. The polarization split element 204 is made of two optical crystals respectively having a crystal axis, which are orthogonal when they are joined. The polarization split element 204 splits the reflection light into two orthogonal polarization components. Then, the split reflection light from the optical disc is reflected by a reflection surface 205, and is incident onto the photoreceptor 207 after being partly diffracted by the first diffraction element 206.
When the tracking servo is performed by the described three beams method, it is necessary to adjust the positions of the sub-beams on the optical disc so as to obtain an accurate tracking signal. The positions are adjusted by rotating the main body 220 of the device about an optical axis 221 of the semiconductor laser 201.
However, the described arrangement of the conventional semiconductor laser package and the optical pickup device has difficulties in downsizing and cost reduction of the device.
In the semiconductor package disclosed in the Japanese Patent Publication No. 3035077, the semiconductor laser chip 104 is disposed in the center of the component bearing surface of the stem 101 and the photodiode 106 is disposed on one side of the semiconductor laser chip 104, which makes the other side of the semiconductor laser chip 104 empty. Therefore, as the free space takes the half of the stem, it results in the difficulties in downsizing and cost reduction of the device.
Also, in the semiconductor package disclosed in the Japanese Unexamined Patent Publication No. 2000-123433, the semiconductor laser chip 201 is disposed in the center of main body 202 and the photoreceptor 207 is disposed on one side of the semiconductor laser chip 201 and the other side of the semiconductor laser chip 201 is empty, thereby causing the difficulties in downsizing and cost reduction of the device.
Further, in this arrangement, polarization split element 204 is disposed between the reflection surfaces 203 and 205 of beam splitter 202, and it makes the size of the device large and therefore the free space also becomes larger.